It is well known that an R-T-B based permanent magnet (wherein R represents a rare earth element, T represents Fe or Fe with part of it substituted by Co) with a tetragonal compound R2T14B as its main phase has excellent magnetic properties, and is a representative permanent magnet with high performance since it was invented in 1982 (Patent Document 1: JP S59-46008A).
In particular, the R-T-B based permanent magnet in which the rare earth element R consists of Nd, Pr, Dy, Ho or Tb has a large magnetic anisotropy field Ha, and is widely used as the permanent magnet material. Of those, the Nd—Fe—B based magnet with Nd as the rare earth element R is widely used in people's livelihood, industries, transportation equipment and the like, because it has a good balance among saturation magnetization Is, curie temperature Tc and magnetic anisotropy field Ha, and is better in resource volume and corrosion resistance than the R-T-B based permanent magnets with other rare earth elements R. However, there are some problems in the Nd—Fe—B based permanent magnet. In particular, the absolute value of the temperature coefficient of the residual flux density is large, and only a small magnetic flux can be provided especially under a high temperature above 100° C. compared to that under room temperature.